The authors describe the methods, organization and results of four large-scale trials of polyvalent, intranasal influenza vaccine conducted in Poland between 1953 and 1957. Vaccination was carried out mainly in industrial establishments, workers' and students' hostels and schools. Very few post-vaccination reactions were seen.In these trials, the formalinized intranasal vaccine, which has the advantage of being easy to administer, gave results not greatly different from those obtained in other countries with injected vaccines or with intranasal live-virus vaccine. The inclusion in the vaccine of a large number of strains, thus giving a broad antigenic spectrum, made it possible to obviate the difficulties involved in isolating a "precursor" strain, and thus made for quicker and more abundant vaccine production before an epidemic.